Transcript for Could the Washington State Mudslide Have Been Prevented?

As we come on the air, a heroic battle is under way to find survivors of that epic mudslide in Washington state. The slide was so big, it registered on the Richter scale. The rescue now hampered by rain and mud so dense, it acts like quicksand, trapping you and pulling you down. Tonight, we're getting a vivid, new portrait the moment the mud came rushing in with lightning speed. ABC's Neal Karlinsky is on the ground for us tonight. Reporter: The terror of the moment. Captured in atlantic 911 calls, minutes of the slide. There's people yelling for help. Today, a small army of search teams, including the national Guard, has poured into this area, to find the missing. Just as rain has made the area more dangerous. Remarkably, this dog was found alive, buried in the wreckage. Dirty, but otherwise okay. At last count, over 100 are unaccounted for, a number that's expected to drop. But little consolation for devastated families waiting for word. We're going to find her. We're going to find her. Reporter: But this is no Normal search. The mud is like quicksand. It's like snow. You stick your foot in, and it sneaks in. Reporter: How did the dog do that? He does the best he can. From jumping from branch-to-branch. Reporter: Geologists say the wet mud is the equivalent of adding hundreds of pounds to each leg. Sticky and thick. You pull your leg out, the boots stay in the mud. Reporter: Experts say this slide was like a mud tsunami, traveling 30 miles per hour. Spreadling out one-square mile. Leaving mud 15 to 30 feet deep. But tonight, there's troubling new evidence this could have been prevented. The 1999 report warned the area had a potential for a large, catastrophic failure. This slide hit the same area in 2006. Officials, today, were quick to respond. We've done everything we could. My heart goes out to all these individuals. We're going to get to the bottom of this. Reporter: Technically, this is still a search effort. But officials stress it is now extremely unlikely anyone will be found alive. It's begun to rain this afternoon. And conditions have really deteriorated, making things that much more hazardous.

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